Over the past several years, there has been an expanding utilization in warehouses of so-called gravity flow rack systems. In such systems, loaded pallets are designed to move by gravity down an inclined guideway from a higher level to a lower level. The pallets are loaded into the rack at the higher level and are unloaded therefrom at the lower level. Although gravity flow storage rack systems have provided substantial improvements in material handling, they have not been without certain drawbacks, one of which has been their cost. In systems employing roller conveyors, a substantial number of rollers are required, as well as suitable braking mechanisms. In systems where pallets are provided with wheels guided on rails, special braking mechanisms are required for the wheels.
Examples of roller conveyor systems, some of which have speed controlling mechanisms associated therewith, are disclosed in the following U.S. Pat. Nos. 4,119,190; 3,627,092; 4,044,876; 3,759,188; 4,054,195; and 3,269,502. Patents disclosing special types of materials for either roller peripheries or railways to control the speed of rail vehicles are disclosed in U.S. Pat. Nos. 3,650,216; 3,651,911; and 3,952,839. Various types of mechanical braking devices for use in controlling the speed of a vehicle moving down an incline are disclosed in the following U.S. Pat. Nos. 3,700,078; 3,576,242; 4,000,796; and 3,871,501. Still further miscellaneous types of vehicle speed control devices are disclosed in U.S. Pat. Nos. 4,023,501 and 3,915,094. Pallets having runners with recessed wheels are disclosed in U.S. Pat. Nos. 2,521,660 and 2,858,774. Moreover, a pallet having means operable automatically to detect a downgrade and to effect a braking action is disclosed in U.S. Pat. No. 3,572,471.
While many of the aforementioned patented devices may function satisfactorily for their intended purposes, there has been an everpresent demand for a vehicle speed control device which is inexpensive to manufacture, relatively maintenance free, and dependable and safe in operation.